How much of a issue is having a internal water pump?

Hello, i'm not sure what you are meaning by "internal" -- the position of the water pump on this vehicle is not unusual -- many engine's have water pumps behind timing belts or chains. In this case, you have the dual chains that must be removed after the timing cover, which is something that only a seasoned technician should be trusted to do. As a result, it's a very long job and costly. That said, there is no evidence of abnormal failures of the water pump on this vehicle. It appears to be a "life of the engine" component, as long as proper maintenance is followed for the cooling system.